1. Field of the Invention
The present invention relates to a developing apparatus which forms a developer image by making developer adhere to an electrostatic latent image formed on an image bearing body, and an image forming apparatus such as a copying machine, a printer, or facsimile equipment that performs image formation by an electrographic system and has the above-described developing apparatus.
2. Related Background Art
Various kinds of developing apparatuses are proposed as a developing apparatus used for an image forming apparatus in each electrographic system. For example, recently, an apparatus performing developing in the configuration of pushing a semiconductive roller or a developing roller, having a dielectric layer on its surface, to a surface layer of a photosensitive body, that is, a contact-one-component-type developing apparatus is proposed.
FIG. 16 is a schematic structural diagram showing an image forming apparatus having a conventional contact-one-component-type developing apparatus (hereinafter, this is simply called a developing apparatus) (this image forming apparatus is an electrographic laser beam printer).
A present image forming apparatus has a drum-type electrographic photosensitive body (hereinafter, a photosensitive drum) 1 as an image bearing body. Around the photosensitive drum 1, a charging roller 2, a developing apparatus 3, a transfer roller 4, and a cleaning blade 5 are arranged, and an exposure device 6 is located outside between the developing device 3 and cleaning blade 5. Furthermore, in the downstream in a transferring material conveying direction of a transferring nip between the photosensitive drum 1 and transfer roller 4, a fixing device 7 is located.
In this embodiment, the photosensitive drum 1 is an organic photosensitive body negatively charged and has a photosensitive body layer (not shown) on an aluminum drum base (not shown), is rotatably driven in predetermined peripheral speed in the direction shown by an arrow A (clockwise), and is uniformly charged in a negative polarity by the charging roller 2 contacting in the rotational process.
The charging roller 2 as charging means rotatably contacts to a surface of the photosensitive drum 1, and uniformly charges the photosensitive drum 1 in predetermined polarity and electric potential by a charging bias applied from a charging bias supply (not shown).
The developing apparatus 3 is a contact-one-component-type developing apparatus performing developing with non-magnetic toner t as one-component developer. The developing apparatus 3 includes a developing roller 11 as a developer bearing body which is located in an opening section of a developing container 10 with facing the photosensitive drum 1 and can be rotate in the direction shown by an arrow (counterclockwise), an elastic roller 12 that can rotate and contacts to the developing roller 11 with pressing the developing roller 11, a control blade 13 that has elasticity and contacts to the developing roller 11, and an agitating member 14 agitating the toner t. The control blade 13 contacts to the developing roller 11 for a press-contacting section of the developing roller 11 and elastic roller 12 in the downstream in a rotational direction of the developing roller 11. The elastic roller 12 rotates in the direction shown by an arrow (clockwise).
The toner t agitated by the agitating member 14 is supplied to a surface of the developing roller 11 by the elastic roller 12 rotating with pressing the developing roller 11. The toner supplied to the surface of the developing roller 11 is conveyed in connection with the rotation of the developing roller 11, is charged by friction in a contacting section of the control blade 13 and developing roller 11, and is laminated on a surface of the developing roller 11. The toner laminated is conveyed by the rotation of the developing roller 11, and manifests an electro static latent image with adhering to the electro static latent image formed on the photosensitive drum 1 in the contacting section with the photosensitive drum 1 (developing section). In addition, toner which does not contribute to the developing on the developing roller 11 is scraped off by the elastic roller 12.
The transferring roller 4 as transferring means forms a transferring nip with contacting to the surface of the photosensitive drum 1 in predetermined pressure, and transfers a toner image on the surface of the photosensitive drum 1 to a transferring material P in the transferring nip between the photosensitive drum 1 and transferring roller 4 with a transferring bias applied from a transferring bias supply (not shown). The transferring roller 4 is rotated in the direction shown by an arrow (counterclockwise).
The cleaning blade 5 removes waste toner that is left on the surface of the photosensitive drum 1 after transferring.
The exposure device 6 includes a laser driver, a laser diode, a polygon mirror, and the like that are not shown. The exposure device 6 forms an electro static latent image corresponding to image information by outputting from the laser diode a laser beam modulated corresponding to a time series electric digital image signal of the image information inputted into the laser driver, scanning the above-described laser beam with the polygon mirror rotating in high speed, and performing image exposure L of the surface of the photosensitive drum 1 through a reflecting mirror (not shown).
The fixing device 7 has a fixing roller 7a and a pressure roller 7b which can freely rotate, and thermally fixes the toner image transferred on a surface of the transferring material P in the fixing nip between the fixing roller 7a and pressure roller 7b by heating and pressurizing the toner image with sandwiching and conveying the transferring material P.
Next, image-forming operation by the above-described image forming apparatus will be described.
In image formation, the photosensitive drum 1 is rotationally driven in predetermined peripheral speed in the direction shown by an arrow A by driving means (not shown), and its surface is uniformly charged by the charging roller 2.
In addition, image exposure L is given by the exposure device 6 on the photosensitive drum 1 that is charged, and an electro static latent image according to image information that is inputted is formed.
Furthermore, as described above, the electro static latent image formed on the photosensitive drum 1 is manifested as a toner image by bonding toner charged in the same polarity as the charged polarity of the photosensitive drum 1 (negative polarity) by the developing roller 11 of the developing apparatus 3 where a developing bias in the same charged polarity as the charged polarity of the photosensitive drum 1 (negative polarity) is applied in a developing section.
Moreover, when the toner image on the photosensitive drum 1 arrives at the transferring nip between the photosensitive drum 1 and transferring roller 4, the transferring materials P such as paper in a cassette 15 is fed every sheet by a pickup roller 16 in accordance with this timing, and is conveyed in the transferring nip by a resist roller (not shown) and the like.
In addition, the toner image on the photosensitive drum 1 is transferred on the transferring material P, which is conveyed to the transferring nip by the transferring roller 4 where the transferring bias in the polarity reverse (positive polarity) to the polarity of the above-described toner is applied, by an electrostatic force occurring between the photosensitive drum 1 and transferring roller 4. Furthermore, the transferring material P where the toner image is transferred is conveyed to the fixing device 7, and is ejected to the outside through a paper output roller 17 after the toner image is thermally fixed by being heated and pressurized on the transferring material P in the fixing nip between the fixing roller 7a and pressure roller 7b, and then a series of image forming operation is finished.
Moreover, waste toner remaining on the surface of the photosensitive drum 1 after toner image transferring is removed by the cleaning blade 5, and is collected in a cleaning container 18.
In addition, recently, against the contact-one-component developing system described above, as disclosed in Japanese Patent Application Laid-Open No. 11-119546 and Japanese Patent Application Laid-Open No. 11-119547, so as to achieve high triboelectric stability and little fog, developing systems to use means for electrically toner charging with using each toner charging roller are proposed.
Here, a developing system using the toner charging roller is shown in FIG. 17. In addition, duplicated description will be omitted by assigning the same numerals to the parts that have the same functions as those in the developing apparatus of the image forming apparatus described above.
This developing apparatus has the toner charging roller 19 that contacts to the developing roller 11 and can freely rotate. A toner charging bias supply (not shown) is connected to the toner charging roller 19. Other configuration is the same as the above-described developing apparatus 3.
In developing operation by this developing apparatus, the toner t agitated by the agitating member 14 is supplied to a surface of the developing roller 11 by the elastic roller 12 rotating with pressing the developing roller 11. The toner supplied to the surface of the developing roller 11 is conveyed in connection with the rotation of the developing roller 11, is charged by friction in a contacting section of the control blade 13 and developing roller 11, and is laminated on a surface of the developing roller 11.
Furthermore, the toner on the developing roller 11 is charged by being given electric charges by the discharge of the toner charging roller 19 where the charging bias is applied. In addition, the laminated toner which is given the charges is conveyed by the rotation of the developing roller 11, adheres to an electro static latent image formed on the photosensitive drum 1 in a contacting section (a developing section) to the photosensitive drum 1, and manifests the electro static latent image.
By the way, as described above, in a developing apparatus having the configuration of charging toner on the developing roller 11 with the toner charging roller 19, the toner charging roller 19 contacts to the developing roller 11, and the toner adheres onto the toner charging roller 19 by applying the voltage higher than a starting voltage, and hence the electrifying property of the toner charging roller 19 drops.
Owing to this, there is such a problem that it is not possible to keep good image quality since stable charges cannot be given to the toner on the developing roller 11.
An object of the present invention is to provide a developing apparatus and an image forming apparatus that can always offer good image quality by preventing adhesion of a developing material to a developer-charging member and always giving stable charges to a developer bearing body and developer.
Another object of the present invention is to provide a developing apparatus and an image forming apparatus that can offer a stable image since it becomes possible to give charges to toner more stably than the above-described case by performing cleaning operation of a toner charging roller before and after image forming operation (developing operation).
Objects except above-described objects and characteristics of the present invention will become clear by reading the following detailed description with referring to accompanying drawings.